Pulsing Microwave Energy: A Method to Create More Uniform Myocardial Temperature Gradients

Abstract

Microwave energy has been proposed as a possible technique to createlarge myocardial lesions. Achieving a uniform myocardial temperaturegradient during microwave ablation may prevent excessive endocardialtemperatures while maintaining temperatures at depth. The goal of thecurrent study was to examine the ability of microwave (MW) pulsing toachieve a more uniform myocardial temperature gradient. Using an in-vitroovine endocardial model, we measured tissue temperature at 0.5-mm, 2.0-mm,and 3.5-mm depths in a circulating saline bath. MW energy was delivered at20 W at 915 MHz for 30 seconds. Pulse configurations of 1 second on–1second off, 3 seconds on-3 seconds off, and 5 seconds on-5 seconds off, with30 seconds of total MW time were compared with 30-seconds continuous.Maximum temperatures at 0.5 mm were significantly lower at 63.2 ±5.89C for the 1-second pulse compared with 83.5 ∓ 7.31C for thecontinuous-energy delivery. Pulse configurations 3 seconds on–3seconds off and 5 seconds on–5 seconds off also resulted in asignificantly lower surface temperature than continuous-energy delivery.However, temperatures at the 2.0-mm and 3.5-mm depth created by the pulsingdelivery were similar to those achieved during continuous-energy delivery.Thus, microwave pulsing achieves a lower endocardial temperature and resultsin a more uniform temperature gradient. These techniques may prevent theexcessive endocardial damage that may result in an increased risk ofthrombus formation and embolization.